81581040 has 160 divisors (see below), whose sum is σ = 283910400. Its totient is φ = 21530880.

The previous prime is 81581029. The next prime is 81581051. The reversal of 81581040 is 4018518.

81581040 is a `hidden beast` number, since 81 + 581 + 0 + 4 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (81581029) and next prime (81581051).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a junction number, because it is equal to n+sod(n) for n = 81580995 and 81581013.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 386535 + ... + 386745.

It is an arithmetic number, because the mean of its divisors is an integer number (1774440).

Almost surely, 2^81581040 is an apocalyptic number.

81581040 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81581040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (141955200).

81581040 is an abundant number, since it is smaller than the sum of its proper divisors (202329360).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81581040 is a wasteful number, since it uses less digits than its factorization.

81581040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 412 (or 400 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 81581040 is about 9032.2223179016. Note that the first 3 decimals coincide. The cubic root of 81581040 is about 433.7069808149.

Adding to 81581040 its reverse (4018518), we get a palindrome (85599558).

The spelling of 81581040 in words is "eighty-one million, five hundred eighty-one thousand, forty".